The present invention relates to an internal combustion engine including a vacuum pump.
Japanese Laid-Open Patent Publication No. 2006-118424, for example, discloses a conventional internal combustion engine including a vacuum pump that generates a negative pressure.
As shown in FIG. 16, a vacuum pump 200 disclosed in Japanese Laid-Open Patent Publication No. 2006-118424 includes a rotor 202, and a housing 203 that accommodates the rotor 202. The rotor 202 is coupled to a camshaft 201 to integrally rotate with the camshaft 201. The housing 203 rotatably supports the rotor 202.
As shown in FIG. 17, a plurality of vanes 204 is attached to the rotor 202 to be slidable in a radial direction of the rotor 202. The plurality of vanes 204 partitions the interior of the housing 203 into a plurality of spaces. A center axis of the rotor 202 is arranged to be decentered with respect to a center axis of the housing 203. Thus, when the rotor 202 is rotated, the capacity of each of the plurality of spaces in the housing 203 is changed. In other words, when the rotor 202 is rotated in the counterclockwise direction in FIG. 17, the capacity of space S1 is increased and the capacity of space S2 is decreased.
The housing 203 includes a suction port connected to a vacuum doubling device of a brake. The suction port is connected to the space S1 in the state shown in FIG. 17. When the capacity of the space S1 is increased, the air in the vacuum doubling device is suctioned into the space S1 of the vacuum pump 200 through the suction port. The negative pressure is thereby generated in the vacuum doubling device.
The housing 203 also includes an air discharge port. The discharge port is connected to the space S2 in the state shown in FIG. 17. Thus, when the capacity of the space S2 is decreased, the air in the space S2 is compressed and the air in the space S2 is discharged from the discharge port. Oil for lubrication is supplied to the vacuum pump 200.
As shown in FIG. 16, the camshaft 201 is formed with an oil feeding passage 205 extending in an axial direction. The rotor 202 is also formed with an oil path 206 extending in the axial direction. The oil feeding passage 205 of the camshaft 201 is connected to the oil path 206 of the rotor 202 by way of an oil feeding pump 207. A penetration path 208 extending in a radial direction of the rotor 202 is arranged in the oil path 206. An oil feeding groove 209 and a communication groove 210 are formed in the housing 203 to communicate with the space in the housing 203. Under the state shown in FIG. 16, the upper end of the penetration path 208 is connected to the oil feeding groove 209 of the housing 203, and the lower end of the penetration path 208 is connected to the communication groove 210 of the housing 203. The communication groove 210 is communicated to atmosphere through a gap between the rotor 202 and the housing 203. The space in the housing 203 is thus communicated to the oil feeding passage 205 and the atmosphere through the oil feeding groove 209 and the penetration path 208, respectively.
Therefore, when the camshaft 201 is rotated accompanying the operation of the internal combustion engine, the rotor 202 is rotated thus generating the negative pressure, and the oil is supplied to the vacuum pump 200 through the oil feeding passage 205 of the camshaft 201. When the operation of the internal combustion engine is stopped and the drive of the vacuum pump 200 is stopped, the oil is taken into the vacuum pump 200 by the negative pressure remaining in the vacuum pump 200. In this case, if a large amount of oil is taken into the vacuum pump 200, the resistance that acts on the vane 204 increases and the vane 204 may break when the vacuum pump 200 is driven again.
Furthermore, in the vacuum pump 200 described above, in the course of the vacuum pump 200 being stopped, the negative pressure in the vacuum pump 200 is consumed as a result of the space in the housing 203 intermittently communicating with the atmosphere through the communication groove 210 and the air being taken into the space in the housing 203. The oil is thus no longer taken into the vacuum pump 200 accompanying the stopping of the internal combustion engine.
In the vacuum pump 200 described in Japanese Laid-Open Patent Publication No. 2006-118424, noise is generated when discharging air from the discharge port. In order to reduce the discharging noise, which becomes the cause of an undesirable noise, it is desirable to suppress the amount of air discharged from the vacuum pump 200 after suctioning the air out from the vacuum doubling device and generating the negative pressure. In the vacuum pump 200 described above, however, the interior of the housing 203 is intermittently communicated with the atmosphere through the communication groove 210 when the rotor 202 is rotated during the operation of the internal combustion engine. Thus, the air is taken into the vacuum pump 200 through the communication groove 210 even during the operation of the internal combustion engine. The discharging noise of the air thus cannot be reduced.